The use of hydrogen additives is not new in HPHT monocrystalline diamonds. It is an important part of the synthesis process and aims to improve the crystalline diamond properties. Hydrogen is a non-reactive metal and is very useful in diamond production. It is present in many natural materials. It is used in many products, such as batteries, and has been used for decades.

The presence of hydrogen in HPHT monocrystalline diamonds has been shown to improve the spectral properties of the material. The study also revealed that boron is a weak acceptor and results in weak absorption peaks. The concentrations of boron ranged from 0.1 to 1 ppm. However, it was determined that the amount of boron in diamonds was not dependent on their sector of growth or the composition of the growth system. The boron is a trace impurity present in the reagents.

The presence of hydrogen additives increases the stability of vacancies. The presence of hydrogen additives in diamond nanoparticles increases their mobility. This effect is achieved by stabilizing the hydrogen surfaces at the six-atomic-layer surface. This vacancy increases the thermodynamic driving force for diffusion.

HPHT monocrystalline diamonds can be classified according to their crystal morphology. Each of them is composed of one or more layers, and varies in size. These layers form the growth surface of the stone. These layers are divided into smaller and larger groups based on their atomic weight.

The growth temperature in HPHT synthesised diamonds can control the morphology of the crystals to some extent. However, the temperature alone cannot produce extremely cubic diamonds. Therefore, a combination of both heat and pressure is required to generate the desired crystals.

High-pressure, high-temperature synthesis is the method of choice for producing single-crystal diamonds. The seed substrates can be prepared by chemical vapor deposition or microwave plasma. The seed substrates are preferably circular or square in shape. The sides of the seeds should be oriented at about 20-degree angles.

Oxygen and hydrogen additives are also important for the growth process. Oxygen is a poorly controlled factor and may account for many of the failures in the growth of high-quality single-crystals. The presence of hydrogen and oxygen in a diamond crystal can indicate an increased concentration of oxygen.

In HPHT monocrystalline diamonds, the CHx modes of sp2 and Sp3 carbon are formed during the fabrication process. During fabrication, the HPHT NDs are exposed to strong acids. However, air annealing removes these groups, resulting in carboxylation and hydroxylation of the diamond core. This removes the sp2-bonded epoxy groups.

This new ND material demonstrates exceptional diamond character even down to 1.1 nm. It may open up new avenues for further research on diamond quantum phenomena. Until now, it was difficult to investigate these phenomena in diamond because of its small size and incommensurate structure. However, with the introduction of annealed HPHT NDs, these properties could be studied in greater detail.

High-quality HPHT NDs can be as small as 3 + 2 nm or even smaller. Moreover, they can be purified and characterized by various techniques. One such HPHT nanodiamond, 1.1 nm, is the smallest man-made nanodiamond to date. In addition, the 1.1-nm diamond remains fully crystalline even after annealing for 30 min at 450 degC.